The invention relates to compositions which contain and methods which utilize lignosulfonates for separating gangue materials from metallic sulfide ores.
Froth flotation is a physical-chemical method of recovering, concentrating, or isolating ground ores. The process involves chemical treatment of an ore pulp or slurry to create conditions favorable for the attachment of selected mineral particles to air bubbles created by passing a stream of air through the ore pulp or slurry. The air bubbles carry the selected minerals to the surface of the pulp and form a stabilized froth which is skimmed from the surface and contains the selected mineral particles. Other non-selected minerals remain dispersed in the pulp or slurry.
Froth flotation has been used as a method for concentrating valuable metallic sulfides for about a century. In froth flotation, sulfide mineral particles in an ore slurry are treated with a processing agent (or collector) that facilitates their flotation and transport by the air bubbles to the surface of the slurry, where the frothed fraction forms. This process has proven to be an economic method of concentrating many simple sulfide ores, where relatively non-selective oils may be used as collectors. However, more complex ores having gangue materials, such as Cu—Fe, Cu—Pb—Zn—Fe, Pb—Zn—Fe, Cu—Zn—Fe, and Cu—Ni—Fe ores require a process that is more selective. Gangue materials typically are considered to include iron containing compounds such as the iron-sulfur compounds pyrrhotite, pyrite, and marcasite. Iron is undesirable because it has to be removed in the smelting stage. Additionally, iron (e.g., in the form of pyrite) can effect efficiency of metal extraction in leaching reactions. Therefore, the less iron an ore contains after a concentration process, then the less costly final recovery of the desired ore will be.
The need to treat such complex sulfide ores has resulted in the development of more selective reagents and reagent combinations. Xanthates have proven to be useful as selective collectors for sulfide minerals. Another common method for obtaining a concentration of desirable metallic sulfides is to depress gangue materials during the flotation of sulfide ore. Sodium cyanide, sodium hydrosulfide, and sodium thiophosphates commonly are used as selective flotation depressants in combination with selective collectors. For example, gangue material (e.g., pyrite) often are depressed by addition of large amounts of calcium hydroxide. In this process, the pH of the bulk slurry is increased and pyrite becomes hydrophilic. Materials rendered hydrophilic tend to be rejected during the flotation process. However, when lime addition is not an acceptable solution (for example where the process must be performed at an intermediate pH, or where iron compounds are not sufficiently rejected even at high pH) then sodium cyanide (or one of the above-mentioned reagents) is often used as a depressant for non-desired minerals, including iron sulfides. However, components like sodium cyanide are hazardous and toxic. As such, chemicals like sodium cyanide are highly regulated and require expensive handling equipment in order to use them in froth flotation.
This invention relates to the use of lignosulfonates during the flotation of sulfide ores. In particular, the invention relates to the use of lignosulfonates derived from hardwood sources. The disclosed lignosulfonate compositions are shown to be effective gangue depressants and provide a method for eliminating the use of hazardous or toxic chemicals, such as cyanides, during the flotation of massive sulfide ores. In particular, the disclosed lignosulfonate compositions are shown to act as a direct replacement for cyanide during the flotation of zinc, lead, and copper ores. These lignosulfonates compositions give equal or superior performance in comparison to other toxic gangue depressants such as sodium cyanide.
U.S. Pat. Nos. 5,693,692; 5,049,612; 4,952,329; 4,880,529; and 4,877,517 disclose gangue depressant compositions that include lignosulfonate. However, the lignosulfonate used in the gangue depressant compositions of these patents, i.e., Kelig 100, differs from the lignosulfonates used in the present application not only functionally but also structurally. First, Kelig 100 is processed in a different way than the lignosulfonates disclosed herein, which substantially increases the polymer's sulfonate and sulfur content and renders the polymer much more hydrophilic than the polymers used in the present disclosure. In addition, Kelig 100 tends to be of higher molecular weight that the hardwood lignosulfonate products disclosed herein. Furthermore, the gangue depressant compositions of these patents are mixtures that include additional ingredients as essential components, such as chemically-modified carbohydrate polymers (e.g., causticized starch), polyacrylates, quebracho, and dextrin. These patent do not disclose specific lignosulfonates that function as efficiently as sodium cyanide in gangue depressant compositions.
U.S. Pat. No. 5,575,334 also discloses the use of lignosulfonates for recovering metal from ore. However, the '334 patent does not disclose the use of specific lignosulfonates as described herein that function as efficiently as sodium cyanide in gangue depressant compositions.
U.S. Pat. Nos. 4,731,113; and 4,645,535 disclose leaching lixiviant compositions that include lignosulfonate. The compositions of these patents are mixtures that include additional ingredients as essential components, such as thiourea compounds and urea, and are used for non-flotation applications. Furthermore, these patents do not disclose specific lignosulfonates as described herein that function as efficiently as sodium cyanide in gangue depressant compositions.